Over pressure on 2 out of 184 rounds?

[Alexander-M]

After shooting 184 rounds of 308 Win consisting of 2X Fired Lapua brass with 185gr Juggernauts, 44.40 gr Varget and KVB-7's in a match, I found two cases that had a black ring around the primer. At first, this black ring was all I saw, and suspected over sized primer pockets. But after taking the picture, below, the ejector marks became obvious, which would indicate an over pressure condition.

In the picture, the two spent cases in questions are in the middle, surrounded by 10 other cases that looks just like the all the other spent cases; i.e., no black ring and no ejector mark.

What could have caused this over pressure?

Powder Charge: I trickle every charge using an FX-120i scale, and while the great majority register 44.40 when I fill the case, I occasionally use a 44.42 gr charge instead of removing one kernel, or starting from scratch. Even if the charge were as high as 44.40 gr, I doubt if it would be enough to cause the signs of over pressure.

Heat: Yes, it was hot, and the barrel was sizzling. However, although I do drop the rounds in the chamber as soon as I eject the spent cases, I make a point of not closing the bolt until I am ready to shoot; I may shoot two to three seconds after I close the bolt. There were occasions when I had to stop to readjust the bipod, or in many more cases, to wipe the sweat off my eyes. But when I did this, I opened the bolt. Perhaps I should have removed the rounds from the chamber in these circumstances?

What is your opinion?

Thanks!

Alex

 

[Highpower-FClass]

Any chance the bullets for those two were seated deeper than the others?

On ejecting the round, I do that if I do not break the shot within the normal timeframe. I put it back in the box and come back to it later. Not sure if it makes a difference or not.

 

[ShootDots]

The brass looks like "Regular" as in "Non-Palma" Lapua brass. The charge is at or near the top of the charge ladder and ALL of your loads, escaped gas rings or not, are on the ragged edge of pressure. If that is your load and it shoots very well, consider moving to the "Palma" S/R primer brass. You will still be on the upper edge, however, the Palma brass can MOST LIKELY handle the pressures you are generating.

 

[M-61]

How many reloads on this brass?

 

[jlow]

I also use 44.3 grains of Varget with the Juggs and Tula LRP in my AT and it has shot well without much fanfare. Your black ring could be a primer defect (I have seen a few of these with Wolf SRM) and I would also have you check your bolt face as it probably got etched.

Have you made sure that all the lube is off your case? Any chance that one or more of your rounds got wet in a rain storm. Both of the above can cause pressure problems as they affect the ability of the case to grip the wall of the chamber and allow more push towards the bolt face.

 

[Alexander-M]

"Any chance the bullets for those two were seated deeper than the others?"
I don't think so, but it is possible. I seat them with a Forster Ultra Micrometer seating die, measure every ten rounds, and they always are within 0.001. These were 2.315 CBTO and were the longest of several depths I tried for the new batch of bullets. None of the others, which started at 2.303, showed these signs.

"The brass looks like "Regular" as in "Non-Palma" Lapua brass. ...."
Correct - regular brass. It has worked very well for me, allowed me to shoot HM in F-T/R, and was fun to shoot. The speed I am getting is around 2765-2780 fps, and I do not remember seeing the black rings around the primers.

"How many reloads on this brass?"
From my original post: " . . . 184 rounds of 308 Win consisting of 2X Fired Lapua brass . . ."

"(1) Have you made sure that all the lube is off your case? (2) Any chance that one or more of your rounds got wet in a rain storm."
(1) I spray-lube, size, trim, clean primer pockets, dunk them in mineral spirits, drain them, and tumble for four hours. I let them sit for a day before I seat the primer and charge them. I believe the lube is off.
(2) No. From the reloading bench, to the plastic case, to the metal cabinet, to range field box, and to the rifle. No rain anywhere.

From now on, when I eject the cases, I will take the second or two that it takes to glance a the primer; especially if the shot was a 'flyer'.

Thank you for your help. I will reconsider everything you said, and will report back if I find the (most likely) answer.

Alex

 

[savagedasher]

Its clear the two cases have impacted the bolt with more pressure.
If the powder charge was the same .
3 things I would look at.
1 case capacity
2 excessive shoulder set back
3 if your not jumping.020 excessive initial ignition start pressure From the powder your using. Larry

 

[danny]

Have these cases ever been used in another rifle?

Danny

 

[boiler_house7]

By chance have the neck walls got thicker on these 2. I have seen where i could just slip a bullet in all fired cases and have had a few cases that would not slip a bullet in and confirmed with a mic on neck thickness and showed pressure increase like these and flyers?

 

[6BRinNZ]

Could be that they sat in the chamber too long (did they go into the group)
Could be that CBTO is a lot closer to the lands than thought and these two actually ended up into the lands. Going into the lands will cause a significant pressure spike which appears to be the case as there are strong ejector marks and leaky primers. i.e. with LRP loads at the top end of pressure, will start to leak after three firings but not necessarily show ejector marks. The presence of two pressure indicators together is a sign of significant pressure.

 

[billlarson]

I believe those are bad primers.............. I contacted Winchester about some I had..... they jacked me around for so long I gave up..... don`t shoot anymore or you`ll cut your bolt face.......
bill

 

[sfinn]

Alex,
I have seen this happen before. For me those cases have been involved in load development and previously exposed to higher pressures. The ejector marks could have been there previously. When they are clean and shiny our older eyes don't always catch em. Since the primers do not show any flattening and look like all others, my opinion is not necessarily pressure, from that particular shot, but loose primer pocket. There again, one would normally notice looseness when seating. Extracting primer will most likely indicate a problem. Also you might measure your extraction ring and compare to other good brass to look for expansion, which causes loose pockets.
Steve Finnell

 

[expiper]

your chamber is oversize at the .200 line,,,it is letting the case heads swell and causing loose primer pokets,,,Roger

 

[DaveTooley]

We all assume every piece of brass out of a box is the same but are they? Weight is the only thing we can check. Why couldn't there be variations in hardness? From what you've told us I think the only explanation is you've exceeded the yield point of those two cases.

 

[DaveTooley]

Roger,
In all my 30+ years building rifles I have never seen a tight base reamer extend the life of primer pockets. All a tight base reamer does is cause extraction problems. When pressure exceeds the yield point of the brass, unsupported brass as in the case head, it moves. It's that simple.

 

[XBBR Shooter]

Your load is not excessive - it is Hodgdon book max (which is conservative).

None of the primers (in any of the cases, including the two in question) show the slightest signs of pressure - in fact the primers show a conservative, mild load. So it is easy to rule out excessive pressure or an over load, or a "spike" (cartridge pressures can rise, but they cannot "Spike")

If the two rounds in question had their bullets jammed into the rifling (and the others did not) then you would see pressure signs on those two primers, which you cannot see.

Since the cases were fired 2 times prior, that leaves only two possibilities.
1 - The two cases in question had soft heads - it is possible. I have had case head failures on new factory loads, where the head expanded so much that the primer dropped out and fell into the action (which is why military cases have crimped-in primers).
2 - An earlier load was excessive and the damage happened before you loaded the cases for this time, and you didn't catch it.

 

[AckleymanII]

Also, Rockwell hardness of brass does vary over the lot. The load is on the ragged edge. Lots of good answers here.

 

[XBBR Shooter]

your chamber is oversize at the .200 line,,,it is letting the case heads swell and causing loose primer pokets,,,Roger

Rodger - Most chambers are over size at the 0.200 line - if this were the cause, almost all fired cases would be ruined on the first firing - and it does not explain the ejector mark.

 

[Alexander-M]

A few answers to your very welcomed comments -
• The cases have never been used in any other rifle. I bought them new, F/L resized them when new, and after every shooting (of course), and had been fired only twice.
• It is possible that the 'damage' may have happened earlier, as when I was testing various seating depths.
• Last night I checked the seating depths of the 16 rounds I have left over, and they were 2.313 ± 0.001.
• When I process these cases, I will measure everything and report back.
• Also, even though no one specifically mentioned it other than when 'brass hardness' was brought up, I have not annealed any of the cases.

Other considerations.
• The barrel may be getting a bit worn (2700 rounds now), and when I measured the bolt-to-lands after 2000 rounds, the distance had enlarged by approximately 0.005, so I started seating the bullets about this distance further out, did some testing, and this worked fine.
• Except for speed testing, which I do at 100 yards with a Magnetospeed, I do all my load development at 600 yards. I shoot five and 10 round groups, and these have consistently had a vertical dispersion under 0.4 MOA with most between 0.3 and 0.25 MOA.
• In matches, the rifle has reliably held a vertical of 0.5 MOA, but I have had the occasional flyer just outside the 10 ring.
• I have won several matches with this rifle using the same loads, including the 2015 Missouri State F-Class with 1578-66X. I did poorly this year at the same match (where I shot the two subject two rounds), mostly my fault, but I found out (too late) that the bipod rail on my rifle was loose. The rail had been epoxied to stock slot, and the heat must have softened it.
• I have a new barrel for the rifle, and have already installed three bolts to secure the bipod rail to the stock. Getting ready for Lodi.
• I will be developing loads for the new barrel, which will have a 10 instead of 11 twist, but everything else will be the same, including the same reamer.

The big uncertainty I have, which I was avoiding bringing up as it has been discussed ad nauseam, is how to measure the distance to the lands. I started to write my concerns on this, which involve using the Stoney Point tool method as well as the split-case method, but it is too long of a subject, so I will start another thread at the risk of being pelted with the expected "Oh, Not Again!" comments.

Thanks!!!!!!

Alex

 

[DaveTooley]

A few answers to your very welcomed comments -
• The cases have never been used in any other rifle. I bought them new, F/L resized them when new, and after every shooting (of course), and had been fired only twice.
• It is possible that the 'damage' may have happened earlier, as when I was testing various seating depths.
• Last night I checked the seating depths of the 16 rounds I have left over, and they were 2.313 ± 0.001.
• When I process these cases, I will measure everything and report back.
• Also, even though no one specifically mentioned it other than when 'brass hardness' was brought up, I have not annealed any of the cases.

Other considerations.
• The barrel may be getting a bit worn (2700 rounds now), and when I measured the bolt-to-lands after 2000 rounds, the distance had enlarged by approximately 0.005, so I started seating the bullets about this distance further out, did some testing, and this worked fine.
• Except for speed testing, which I do at 100 yards with a Magnetospeed, I do all my load development at 600 yards. I shoot five and 10 round groups, and these have consistently had a vertical dispersion under 0.4 MOA with most between 0.3 and 0.25 MOA.
• In matches, the rifle has reliably held a vertical of 0.5 MOA, but I have had the occasional flyer just outside the 10 ring.
• I have won several matches with this rifle using the same loads, including the 2015 Missouri State F-Class with 1578-66X. I did poorly this year at the same match (where I shot the two subject two rounds), mostly my fault, but I found out (too late) that the bipod rail on my rifle was loose. The rail had been epoxied to stock slot, and the heat must have softened it.
• I have a new barrel for the rifle, and have already installed three bolts to secure the bipod rail to the stock. Getting ready for Lodi.
• I will be developing loads for the new barrel, which will have a 10 instead of 11 twist, but everything else will be the same, including the same reamer.

The big uncertainty I have, which I was avoiding bringing up as it has been discussed ad nauseam, is how to measure the distance to the lands. I started to write my concerns on this, which involve using the Stoney Point tool method as well as the split-case method, but it is too long of a subject, so I will start another thread at the risk of being pelted with the expected "Oh, Not Again!" comments.

Thanks!!!!!!

Alex

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